The present invention relates generally to underground drilling machines. More particularly, the present invention relates to reamers for use in horizontal directional drilling.
Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular.
A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground.
In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore.
The diameter of the pilot bore so constructed typically must be enlarged. To accomplish this, a reamer (sometimes called a backreamer) is attached to the drill string which is pulled back along the path of the pilot hole, thus reaming out the hole to a larger diameter. The reamer usually includes a reaming or cutting surface on which is mounted cutting teeth or other cutting or grinding elements. It is also common to attach a utility line or other conduit product to the reamer so that the product is pulled through the hole behind the reamer as the reamer enlarges the hole.
A backreamer, then, may perform several functions including: mechanically cutting, grinding and loosening the soil to enlarge the pilot hole diameter, directing drilling fluid to assist in the cutting action, mixing the loosened soil with the drilling fluid such that the resulting slurry is a consistency that will flow out of the bore when displaced by whatever product is to be pulled in, and transferring the longitudinal force required to pull the product through the hole.
The amount of torque necessary to rotate a backreamer depends on several factors which include: the outer diameter of the backreamer, the difference between the diameter of the pilot hole and the outer diameter of the backreamer, the type of soil, the speed at which the backreamer is being rotated, and the longitudinal force being applied to the backreamer.
When utilizing standard backreaming techniques a backreamer is pulled longitudinally along the path of the pilot bore. Under certain conditions, however, the backreamer may tend to deviate from the path defined by the pilot bore. For instance, typically the pilot bore and drill string lie in an arcuate shape. Therefore the longitudinal force being exerted on the drill string tends to straighten the drill string, especially when soil conditions require increased levels of force on the drill string. This straightening tendency can affect the location of the backreamer by pulling the reamer higher. In some jobs the backreamer may move as much as 12 to 18 inches from the pilot bore. Such inaccuracy can have negative effects particularly when a utility or natural obstacle such as a river is being avoided.
In other situations, where large diameter bores are being formed, the weight of the backreamer can cause deviation from the pilot bore. A backreamer is typically moved longitudinally along the pilot bore at a rate in proportion to the drilling fluid being pumped to the reamer and out of the pilot bore. Therefore, longitudinal progress may be very slow. A heavy backreamer in the right soils will tend to drop lower than the pilot bore as it rotates quickly but moves slowly longitudinally.
In still other situations, varying ground conditions can cause the backreamer to move. For instance where there are distinct strata of significantly varying types of soils, the transition zones between one strata and another can cause such a deviation. In another situation there may be random obstacles like relatively large rocks interspersed within soils, that likewise can cause significant deflection of the backreamer.
Deviation from the pilot bore during backreaming is especially problematic in applications where maintaining a desired grade is important. The installation of sewer lines is one such application. The forces exerted on the backreamer by the sewer line being pulled into the bore behind the backreamer as well as the forces exerted by the drill string to cut large diameter holes make it difficult to maintain the desired grade established by the pilot bore. Variations in soil conditions can likewise make it difficult to maintain the desired grade and hole straightness.
One aspect of the present invention relates to a backreamer adapted with an hydraulic cylinder for steering the reamer as it is pulled or pushed through a pilot bore. The hydraulic cylinder is coupled to both a carrier frame and a carrier frame housing so that by action of the hydraulic cylinder the carrier frame may be tilted relative to the carrier frame housing thereby increasing control and steering during the reaming process.
Another aspect of the present invention relates to a backreamer having an elongated carrier frame housing which operates to make deviation from the pilot bore more difficult. An increased ratio of length to diameter assists the backreamer in following the pilot bore and maintaining a desired grade.
Another aspect of the present invention relates to a backreamer adapted with two sondes for monitoring the position of both ends of the backreamer in order to assist in steering the backreamer by determining the orientation of the backreamer. One sonde is located at a proximal end of the backreamer, and the other sonde is located at a distal end of the backreamer.
Another aspect of the present invention is directed toward a method of backreaming which includes the steps of: providing a backreamer with an hydraulic cylinder which operates to tilt a reaming body or surface of the backreamer relative to a carrier frame housing of the backreamer; running an hydraulic line from a source outside the bore to the hydraulic cylinder; and operating the hydraulic cylinder to assist in steering the backreamer during the reaming process.
Another aspect of the present invention is directed towards a method of backreaming including the steps of providing a backreamer with two sondes, one placed at the proximal and distal ends of the backreamer and using the sondes to monitor the position and angle of the backreamer to assist in steering the backreamer and thereby maintaining a desired course along a pilot bore.
Another aspect of the present invention is directed toward including a laser sensitive guidance system within the backreamer to automatically and accurately guide the backreamer along a desired bore.
Another aspect of the present invention relates to a method for maintaining a desired grade for a backreamer along a pilot bore by guiding the backreamer with a laser beam directed along the desired grade and a laser sensitive target disposed within the backreamer.
Another aspect of the present invention relates to a backreamer adapted with a non-rotating carrier frame and rotating front cutting structure, a controller, a transducer capable of measuring mechanical deflection of the front cutting structure relative to the carrier frame, a steering system capable of directing the front cutting structure, a free motion connection with the product being installed into the ground, and a communication link to the drill rig.
Another aspect of the present invention relates to a backreamer adapted with a non-rotating carrier frame and a rotating cutting structure further adapted such that whenever the formed bore deviates from a straight cylindrical hole there is a measurable deflection of movement within the carrier frame and cutting structure.
Another aspect of the present invention relates to a joint between a carrier frame of a backreamer and a front cutting structure that allows the front cutting structure to shift into an eccentric position relative to the carrier frame such that the cutting structure will advance more aggressively into a direction of the material that is more difficult to cut.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.